Rate Constant Determination for Saponification in Batch & CSTR February 17, 2005 Presentation by Trevor Binney Group Members Jay Berndt Me Eric Houchin Operations Manager Team Leader Safety Coordinator Presentation Plan • Familiarize audience with saponification • Discuss the project objectives • Overview of process and equipment used • Batch and CSTR kinetic data results • Difficulties encountered during lab work • Give recommendations for future work • Answer any questions the audience have Nomenclature • CSTR- Continuous Stirred Tank Reactor • EtAc- Ethyl Acetate • NaAc- Sodium Acetate • EtOH- Ethyl Alcohol (Ethanol) • PPE- Personal Protective Equipment • Soln- Solution • Xa- Extent of Reaction of NaOH • Conc- Concentration in mol/L • Ca- mol/L NaOH What is Saponification, and what is it used for? • http://www.dictionary.com/ defines saponification as: A reaction in which an ester is heated with an alkali, such as sodium hydroxide, producing a free alcohol and an acid salt, especially alkaline hydrolysis of a fat or oil to make soap. • EtAc + NaOH NaAc + EtOH • CH3COOC2H5 + NaOH CH3COONa + C2H5OH • Saponification is primarily used for the production of soaps. Project Objectives Our team was asked to meet several goals while running saponification experiments 1. Develop conductivity calibration curves for the reactants used in the process. (NaOH & EtAc) 2. Verify feed concentration through standardization using titration 3. Determine the true rate constant for reaction in a batch reactor 4. Obtain reaction rate data for the CSTR as a function of the solution residence time Safety Considerations • NaOH- Corrosive • EtOH & EtAc- Flammable • EtAc will corrode various plastics • Standard PPE worn, as well as face shield and rubber gloves for handling dangerous chemicals. • Clean up spills and broken glass immediately • Be aware of where other people in the lab are • Open windows for ventilation and work under the fume hood when mixing solutions Assumptions • Conductivities EtAc & EtOH negligible • Solution inside the CSTR is well mixed • Solution inside batch reactor well mixed • Ethyl acetate bottle wasn’t contaminated • Liquid pulled from the “1 M” EtAc is 1 M • The CTSR flow meters were accurate • Conductivity linearly proportional to Conc Conductivity Probe Calibration Conductivity Probe Calibration NaOH Conductivity vs Concentration 60 50 y = 214.03x Conductivity (mho) 40 30 Literature Data 20 Calibration 10 Linear (Literature Data) 0 0 0.05 0.1 0.15 0.2 0.25 0.3 Molarity NaOH Xa & Conc Solved w/ Conductivity • NaOH conductivity: 214*(conc NaOH) mS/m • NaAc conductivity: 78*(conc NaAc) mS/m • EtAc & EtOH conductivity: negligible • Overall conductivity: Ca0*(214-136*Xa) • Where Xa = (Ca0 – Ca) / Ca0 Continuous Stirred Tank Reactor CSTR procedure 1. Enter setpoint temperatures using set point 2 2. Drain reactant tanks as much as possible 3. Prepare three liters of reactant solutions 4. Fill tanks equally and heat to set temp 5. Make sure the bottom reactor drain is closed 6. Turn on the CSTR stirring device 7. Open the flow valves to equal levels 8. Wait until SS reached and record conductivity using a calibrated conductivity probe Batch Reactor and Heating Bath Batch Procedure 1. Preheat bath to desired reaction temp 2. Prepare the NaOH and ethyl acetate solutions 3. Fill two erlenmeyer flasks, one with NaOH and the other with EtAc 4. Allow reactants to heat to desired temp 5. Pour one flask into the other submerged flask 6. Using the conductivity probe, record conductivities of the solution every 15 seconds 7. Record data until the conductivity stabilizes Equations Used for Data Analysis • Arrhenius’ law: k = k0e-E/RT • ln(k2/k1)=E/R*(1/T1 – 1/T2) • Ca0*(214-136*Xa) • Xa = (Ca0 – Ca)/Ca0 • Ca = (Cond/Ca0 – 214)*Ca0/136 + Ca0 Results and Conclusions Results and Conclusions Results and Conclusions • (k) Determined rate constant for saponification • Experimental k = 0.178 L/mol*sec @ 30 °C • Experimental k = 0.192 L/mol*sec @ 45 °C • As listed in in the Bulletin of the Chemical Society of Japan k = 0.112 L/mol*sec • According to this source, the rate constant we determined was about 59% too large • A possible reason for this is that the EtAc solution concentration was higher than predicted CSTR Results and Conclusions Data recorded was very inconsistent – For equal feed concentrations, we had runs that yielded conductivities of 6-7 mS and also 3 mS/m, with no results falling in between • Reagent bottle contamination? • Inability to completely drain feed tanks • Difficulty in maintaining stirring speed – CSTR operations were abandoned for the final lab period to focus on Batch data Temperature Dependence Results Multiple trials were run at both 30 & 45 °C • Arrhenius’ law: k = k0e-E/RT • Rewritten: ln(k2/k1)=E/R*(1/T1 – 1/T2) • R = 8.314 J/mol*K • E = Activation energy of this reaction We were unable to find the value for E in literature k30 = 0.178 L/mol*sec < k45 =0.192 L/mol*sec Experimental E = 4040 J/mol Overall Conclusions • Saponification rxn is a 2nd order reversible reaction – (1/Ca vs time linear at low time) • -Ra = k*Ca*Cb • Considerable error comparing experimental rate constant to that in literature • Batch data fairly reproducible and precise • CSTR data and operation inconsistent Difficulties Encountered During Lab • Creation and mixing of ethyl acetate solns – Attempted creation of “1 M” stock solution • Attempted to dissolve 9.6 g EtAc/100 mL • Max Solubility of EtAc in water is 8 g/100 mL – Possible reagent bottle contamination • Evident through formation of unknown precipitate • CSTR temperature reading inconsistency • Inability to completely drain CSTR tanks Recommendations For Future Work • Do research before entering the lab • Become familiar with analytical equipment • Begin trials with CSTR as early as possible • Split up tasks for each person to do during lab prior to running the labs • Make an in depth Design of Experiment before entering the lab References • Levenspiel, Octave. Chemical Reaction Engineering, Third Edition. USA: John Wiley & Sons, 1999. • Levenspiel, Octave. The Chemical Reactor Omnibook. Corvallis, OR: OSU Book Stores, 2002. • Pecaj, Arta. Personal Interview. February 16, 2005. • Tsujikawa, H. and Inoue, H. 1965. The Rate of the Alkaline Hydrolysis of Ethyl Acetate. Bulletin of the Chemical Society of Japan. 39: 1837-1839 • http://www.woodlandsinstruments.com/conductivity_ values.htm Questions ??
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